1. Field of the Invention
The present invention relates to a communication system which voice-code-compresses and transmits a voice signal from a voice terminal apparatus of a telephone terminal apparatus or a private branch exchange (hereinafter referred to as PBX) or the like, and particularly to a DTMF signal transmission method and communication apparatus for accurately transmitting a dual tone multi-frequency (hereinafter referred to as DTMF) signal including a push button (hereinafter referred to as PB) signal.
2. Description of the Related Art
Up to now, a communication system which voice-code-compresses and transmits a voice signal to the opposite side by means of a communication apparatus such as a multiplexer and the like has also voice-code-compressed and transmitted a DTMF signal such as a PB signal and the like sent from a telephone terminal apparatus as well as an ordinary voice signal to the opposite communication apparatus. That is to say, a communication apparatus at the transmission side voice-code-compresses and transmits as an ordinary voice signal a DTMF signal without paying a particular attention, and on the other hand, a communication apparatus at the reception side voice-code-expands and restores the received voice-code-compressed signal to a voice signal (DTMF signal) and sends it to a voice terminal apparatus of a PBX or the like, and the voice terminal apparatus judges and recognizes the code of the DTMF signal and performs a specified operation.
Like the above-mentioned prior art, however, in case of compressing and expanding a DTMF signal as one of voice signals, there has been a problem that a DTMF signal (voice signal) expanded by a communication apparatus at the reception side is out of a reception rule and is sometimes not recognized as a DTMF signal by a voice terminal apparatus side of a PBX and the like.
And in case of transmitting a DTMF signal, there has been a problem that since a communication apparatus side which has received a DTMF signal needs a judgement time for judging the DTMF signal and the DTMF signal is transmitted to the opposite voice terminal apparatus as a voice signal during the judgement time, a DTMF signal restoring side obtains a DTMF sound by expanding a voice-code-compressed DTMF signal and then restores a DTMF signal obtained by decoding a DTMF signal and thus the DTMF sound obtained by expanding a voice-code-compressed signal sometimes comes to be out of a reception rule for a DTMF signal and sometimes is not recognized as a DTMF signal by a voice terminal apparatus side of a PBX or the like.
An object of the invention is to provide a DTMF signal transmission method and communication apparatus capable of judging/recognizing a DTMF signal without error by means of a communication apparatus at the reception side (voice terminal apparatus) even in case of transmitting the DTMF signal by means of a communication apparatus for performing a voice code compression.